1. Field of the Invention
The present invention relates to bullets/projectiles (hereinafter referred to as bullets) and cartridge cases. More particularly, the present invention relates to lead free, composite polymer based bullets and cartridge cases, and a method of manufacturing the same.
2. Description of Related Art
It is well known in the industry to manufacture bullets and corresponding cartridge cases from either brass or steel. Typically, industry design calls for materials that are strong enough to withstand extreme operating pressures and which can be formed into a cartridge case to hold the bullet, while simultaneously resist rupturing during the firing process.
Conventional ammunition typically includes four basic components, that is, the bullet, the cartridge case holding the bullet therein, a propellant used to push the bullet down the barrel at predetermined velocities, and a primer, which provides the spark needed to ignite the powder which sets the bullet in motion down the barrel.
The cartridge case is typically formed from brass and is configured to hold the bullet therein to create a predetermined resistance, which is known in the industry as bullet pull. The cartridge case is also designed to contain the propellant media as well as the primer.
The bullet is configured to fit within an open end or mouth of the cartridge case and conventionally includes a groove (hereinafter referred to as a cannelure) formed in the mid section of the bullet to accept a crimping action imparted to the metallic cartridge case therein. When the crimped portion of the cartridge case holds the bullet by locking into the cannelure, a bullet pull value is provided representing a predetermined tension at which the cartridge case holds the bullet. The bullet pull value, in effect, assists imparting a regulated pressure and velocity to the bullet when the bullet leaves the cartridge case and travels down the barrel of a gun.
Furthermore, the bullet is typically manufactured from a soft material, such as, for example only, lead, wherein the bullet accepts the mouth of the cartridge being crimped to any portion of the bullet to hold the bullet in place in the cartridge case, even though the cartridge case is crimped to the cannelure of the bullet.
The propellant is typically a solid chemical compound in powder form commonly referred to as smokeless powder. Propellants are selected such that when confined within the cartridge case, the propellant burns at a known and predictably rapid rate to produce the desired expanding gases. As discussed above, the expanding gases of the propellant provide the energy force which launches the bullet from the grasp of the cartridge case and propels the bullet down the barrel of the gun at a known and relatively high velocity.
The primer is the smallest of the four basic components used to form conventional ammunition. As discussed above, primers provide the spark needed to ignite the powder which sets the bullet in motion down the barrel. The primer includes a relatively small metal cup which contains a priming mixture, foil paper, and relatively small metal post, commonly referred to as an anvil.
When a firing pin of a gun or firearm strikes a casing of the primer, the anvil is crushed to ignite the priming mixture contained in the metal cup of the primer. Typically, the primer mixture is an explosive lead styphnate blended with non-corrosive fuels and oxidizers which burns through a flash hole formed in the rear area of the cartridge case and ignites the propellant stored in the cartridge case. In addition to igniting the propellant, the primer produces an initial pressure to support the burning propellant and seals the rear of the cartridge case to prevent high-pressure gases from escaping rearward. It should be noted that it is well known in the industry to manufacture primers in several different sizes and from different mixtures, each of which affects ignition differently.
The cartridge case, which is typically metallic, acts as a payload delivery vessel and can have several body shapes and head configurations, depending on the caliber of the ammunition. Despite the different body shapes and head configurations, all cartridge cases have a feature used to guide the cartridge case, with a bullet held therein, into the chamber of the gun or firearm.
The primary objective of the cartridge case is to hold the bullet, primer, and propellant therein until the gun is fired. Upon firing of the gun, the cartridge case seals the chamber to prevent the hot gases from escaping the chamber in a rearward direction and harming the shooter. The empty cartridge case is extracted manually or with the assistance of gas or recoil from the chamber once the gun is fired.
There are three common cartridge case designs that are well known in the industry. In particular, a bottleneck cartridge case 10 shown in FIG. 1 is used with rifles. A straight inner walled cartridge case 20 shown in FIG. 2 has inner walls of the cartridge case that are substantially parallel with a longitudinal axis of the case, which is commonly used with pistols. A tapered straight inner walled cartridge case 30 shown in FIG. 3 has inner walls that are oblique or not parallel relative to the longitudinal axis of the case and is commonly used with revolvers.
As shown in FIG. 1, the bottleneck cartridge case 10 has a body 11 formed with a shoulder 12 that tapers into a neck 13 having a mouth at a first end. A primer holding chamber 15 is formed at a second end of the body opposite the first end. A web area 16 separates a main cartridge case holding chamber 17, which contains a propellant, from the primer holding chamber 15, which communicate with each other via a flash hole channel 18 formed in the web area 16. An exterior circumferential region of the rear end of the cartridge case includes an extraction groove 19a and a rim 19b. 
As can be seen in FIG. 2, the straight inner walled cartridge case 20 does not include a shoulder that tapers to a neck 23 at the first end of the cartridge case 20. Furthermore, the straight inner walled cartridge case 20 does not have a rim significantly larger than a case diameter D20 and is commonly referred to as a rimless case in the industry. Likewise, the tapered straight wall cartridge case 30 shown in FIG. 3A differs from the cartridge case 20 shown in FIG. 2 as it has interior tapered walls and a rim 39b larger than a case diameter D30.
FIG. 3B is an enlarged view of a lip lock 32 provided in the vicinity of the mouth 34 of the cartridge case 30. The lip lock 32 includes a first, generally straight portion 32a, which is orthogonal to a longitudinal axis of the case 30; a second, generally straight portion 32b, which is parallel to the longitudinal axis of the case 30 and orthogonal to the first straight portion 32a; and a slanted portion 32c, which is oblique relative to the longitudinal axis of the cartridge case 30 and both straight portions 32a and 32b. The lip lock 32 is used to securely grip a bullet (not shown).
Typically, manufacturers must take as many as twenty three (23) steps to manufacture a brass cartridge case from a rolled strip of brass material. During loading, which is the step where the cartridge case is loaded with the powder and bullet, the brass cartridge case is crimped to the bullet so that the bullet is held therein. It is well understood that crimping is necessary to assist in creating the pressure needed for satisfactory ballistic performance.
Ballistic performance is a set of measurable events resulting from the combination of a particular bullet weight placed over a particular propellant charge to be ignited by a priming method of predetermined size that establishes the pressure build up needed to propel the bullet at a desired velocity.
As shown in the schematic diagram of FIG. 4, case walls 41a and 41b of the brass cartridge cases 40 are typically crimped at a mouth 44 onto the bullet B to hold the bullet B in place. The contact surface is the wall thickness of the brass cartridge case 40 at the point the cartridge case 40 is crimped.
Alternatively, the cartridge case 50 may be tapered from a rear end 51 to the mouth 54, as shown in FIG. 5, so as to create a press fit P at the mouth 54 of the case 50, which causes the bullet B to be held in place over a larger bearing surface.
In yet another alternative, adhesives may be used to hold the cartridge case and bullet assembly together to assist in providing a desired pressure. Some commercial, law enforcement, and military firearms ammunitions are assembled with adhesives to provide an increased pressure where a simple crimping step is not sufficient.
In the late 1990's it was reported that the military would begin the use of so-called green bullets. Supposedly, such green bullets would be made of high-density materials, such as tungsten, mixed with lighter materials, such as tin and zinc. It was also reported that tungsten-nylon cores could be used. However, no specific range of ingredients was ever provided. It should be noted that the green bullets were fabricated with copper jackets. See Mikko, Assoc. of Firearm and Tool Mark Exam. Journ., vol. 31, No. 4, Fall 1999; USA Today, “‘Green’ Army bullets to get the lead out,” and Environmental Update, Fall 1999.
Several patents for green bullets have been issued.
For example, WO 88/09476 to Booth discloses a bullet made of materials having a specific gravity of 3 to 7, a matrix of plastic material, such as nylon 6 or nylon 6/6, and a filler of a finely divided metal, such as copper, bronze or tungsten. In the preferred compositions, Nylon is incorporated in an amount of 8% or 11% by weight. The filler material is present in essentially the remainder amount. Either one of the nylon 6/6 or nylon 6 is explained as being used in amounts of up to 20% by weight. Booth does not disclose using both nylon materials together in the same bullet.
U.S. Pat. No. 5,616,642 to West et al. discloses a bullet containing a high density powder, such as copper, tungsten, bismuth, ceramic or stainless steel, in an amount of at least 85%, dispersed in a polyester matrix, such as polybutylene terephthalate or polyethylene terephthalate.
U.S. Pat. No. 6,048,379 to Bray et al. discloses a bullet made of tungsten, a fiber, such as stainless steel, copper, aluminum, nylon, Kevlar, Spectra, nickel, glass or carbon, and a binder material, such as nylon 12 or a polyester elastomer. Bray et al. indicate nylon 6/6 and nylon 6 are resins that are not suitable as binders. See column 10, lines 18–19.
U.S. Pat. No. 6,257,149 to Cesaroni discloses a bullet having a core made of a polymer, such as ethylene/methacrylic acid copolymer ionomers, polyetherester elastomers or polyamides, such as nylon 11 or nylon 12, and a jacket made of copper, nylon 6/6, nylon 6/12, nylon 4/12, flexible nylon, nylon 6 or nylon 11.
As stated above, the test for all methods of holding the bullet within a cartridge case is commonly known as bullet pull. The Sporting Arms and Ammunition Manufactures Institute (hereinafter referred to as “S.A.A.M.I.”) established a bullet pull for all calibers that creates a desired pressure to deliver the desired ballistics. The United States Military has also established bullet pull specifications that achieve the products desired ballistic performance.